Apparatus for producing one-piece multifocal lens blanks



March 2, 1943. F. E. DUCKWALL 2,312,529 APPARATUS FOR PRODUCING AONE-PIECE MULTIFOCAALENS BLANK Original Filed May 17, 1940 2Sheets-Sheet l Flq. T'

March 2, 1943. F. E. DUCKWALL 2,312,529"

APPARATUS FOR PRODUCING A ONE-PIECE MULTIFOCAL LENS BLANK Original FiledMa y 1'7, 1940 I 2 Sheets-Sheet 2 flung an I INVENTOR. fem/Ki. flue/(muL Patented Mar. 2, 1943 UNITED STATES PATENT OFFICE APPARATUS FORPRODUCING ONE-PIECE MULTTFOCAL LENS BLANKS Frank E; Duckwall,Indianapolis, Ind., assignor to Continental Optical Company, Inc.,Indianapolis, Ind., a corporation (Cl. 511Z7) 7 Claims.

This invention relates to the apparatus and method employed in.producing one-piece bifocal or trifocal lens blanks and lenses, andparticularly that type of lens having anon-circular segment forproviding the near vision field, and in some modifications, anintermediate vision field, being a division of my copen-dingapplication, Serial No. 335,810, filed May 17, 1940, for Apparatus andmethod for producing a one piece multifocal lens blank and lens.

In the actual commercial production of such lenses, it. has been foundthat the use of a cam button secured to the lens for directlycontrolling and guiding the grinding and polishing buttons is the mostpractical and satisfactory means of producing such a lens. But in theuse of such cam button, difiiculty has been emerienced in conforming thegrinding and polishing action to the exact boundary line or demarcationbetween the two fields. This. is for the reason that wherein the cambutton lies on said line, it is impossible to carry the grindingoperation sharply thereto, since a film of rouge and dust becomesinterposed and embedded about the cam button, resulting in a minutedepressed groove being produced which may be due. to the wedging actionof the cam and button.

To overcome the above, there is employed an undercut cam button having araised tool engaging cam of the area and shape desired for the finishednear vision field, and spaced from the surface thereof by a securingblock spaced inwardly from its tool engaging surface.

It is the purpose of this invention to provide a method and apparatusfor accurately positioning the cam upon the lens blank and securing itthereto, and particularly a cam button of the above-described character.

The full nature of the invention will be understood from theaccompanying drawings and the following description and claims:

Fig. 1 is a plan view of a lens blank with the inner and outer surfacesrough ground.

Fig. 2 is an enlarged section taken on the line 2-2 of Fig. 1.

Fig. 3 is the same as Fig. 2, showing a modified form.

Fig. 4 is the same as Fig. 1 showing the cam button secured over aportion of the inner field.

Fig. 5 is an enlarged section taken on the line 5-5 of Fig. 4.

Fig. 6 is a plan view of the finished lens showing the finishednon-circular inner field in full lines and the removed portion thereofin dotted lines.

Fig. 7 is, a plan view of the cam button centering device.

Fig. 8 is. a section taken on, the line 8-8 of Fig. '7.

In the drawings, there is illustrated a full uncut. lens blank l0 uponwhich there has been roughly ground a distance vision field A and acentrally ground and finished concentric inner near vision field B.

In the manner hereinafter described, a cam button H is secured to aportion of the field B. as illustrated in Figs. 4 and 5, said buttonhaving a tool-engaging cam surface [2 spaced above the surface of theblank and secured thereto by an inset block portion I3. The cam surface12 is of the shape desired for the finished segment of the lens whichcomprises the inner near vision field, whereby a grinding or polishingtool may be applied to the exposed surface of the blank for grinding andpolishing said surface to produce a one-piece bifocal lens having anon-circular near vision field B, as shown in Fig. 6.

In this operation, that portion of the blank indicated by dotted linesin Fig. 5 is ground and polished away to provide the finished distancevision field A, leaving a shoulder l 4 and a merged arcuate boundaryline l5 between the fields of the finished lens, the shoulder portionI4. beingv substantially fiat and located at approximately the optical;center of the two fields for minimizing the image jump therebetween.

As previously stated, the problem here involved. and to which thisinvention is directed, lies in the complete elimination of any vestigeof the original boundary line indicated at. l6, while simultaneouslyeffecting the smooth merging of the fields along the arcuate boundaryline indicated at 15.

For securing the cam button to the lens, it is provided with asubstantially centrally positioned orifice I! extending therethrough,through which a cementing shellac is introduced when the cam has beenaccurately positioned. For positioning the cam, reference is made toFigs. '7 and 8 illustrating the cam setting tool. After the cam has beenset by said tool and the shellac poured in place, the tool with theblank is placed in a suit able furnace and heated so that the shellacpassing from the orifice I 1 between the adjacent surfaces of the cambutton and lens, will be hardened in place to firmly cement it. V

The cam setting tool comprises an annular holder 20 having a peripheralseat 2| upon which the blank I0 is placed. Vertically movable arms 22are mounted for vertical adjustment upon the in extended position withrespect to the block under tension of a spring 21. Said positioninghead, through the block, is adjustable radially of the blank andlongitudinally of its supporting arm 22 by an adjusting screw 28 havingthreaded engagement with the block 24 and rotatably supported by abearing 29 extending longitudinally of the arm 22. Said screw 28 hassecured thereon for adjusting purposes a thumb nut 30.

Upon the blank being mounted in the holder 20, the operator, by means ofa magnifier and proper illumination, adjusts the heads 26 to a positionso that their blank engaging edges accurately lie tangentially withthree segments of the boundary line l6 about the inner field B, as

' shown in Fig. 7. The operator then selects a cam button 12 of theproper size to snugly fit between the three positioning buttons 26.Since in grinding the field B, there may be some slight variation indiameter, the operator is provided with several buttons l2 of slightvariation in size, selecting the button which most closely fits withinthe positioned heads 26.

With the button l2 so positioned, and while snugly nesting between theheads 26, the shellac is poured into the aperture I1 and the entire camlocating tool is placed in the furnace to effect the hardening of theshellac to firmly secure the cam to the blank for the following grindingand polishing operations.

The invention claimed is:

1. An apparatus for positioning a blanking out cam button on amultifocal lens blank having a boundary line separating its fields,comprising a holder for said blank having a seat for centering the blankthereon, a series of positioning heads each having a surface engageableby the cam button and extending to the surface of the blank, a bracketassociated with each of said heads adjustably mounted on said holder,and a universal yielding and adjustable mounting on each of saidbrackets adapted to support and adjust the respective heads thereon toeffect the accurate positioning thereof relative to said boundary line,whereby said heads may receive and position said cam button foralignment therewith.

2. An apparatus for positioning a blanking out undercut cam button on amultifocal lens blank having a boundary line separating its fields andwherein the cam surface of said button is spaced therefrom, comprising aholder for said blank having a seat for centering the blank thereon, aseries of positioning heads each having a peripheral surface engageableby the spaced surface of the button and extending to the surface of theblank parallel to the axis thereof, a mounting on said holder for eachof said heads, and a radially adjustable support carried by saidmountings respectively operable to effect the accurate positioning ofsaid heads on said boundary line for locating the spaced cam surface ofthe button in projected relation thereto.

3. An apparatus for positioning a blanking out cam button on amultifocal lens blank having a boundary line separating its fields,comprising a holder for said blank formed to provide a centering seattherefor, a series of brackets adjustably mounted on said holder toextend over. the blank when seated thereon, a positioning headassociated with each of said brackets, a universal spring pressedmounting adapted to support each of said heads on its respective bracketin surface,

engagement with the blank, and a screw adjustably supported by each ofsaid brackets operably connected with its respective mounting to effectthe setting of the head in alignment with said boundary whereby saidheads are adapted to locate the button therebetween in operativerelation to said boundary.

4. An apparatus for positioning a blanking out cam button on amultifocal lens blank having a circular boundary line separating itsfields, comprising a holder for said blank, a plurality of locatingheads mounted on said holder engageable by said button to control thepositioning thereof in alignment with a portion of said boundary line,and an adjustable mounting on said holder for each of said headsoperable to move them radially of said blank into button aligningposition.

5. An apparatus for positioning a blanking out cam button on amultifocal lens blank having an outer vision field and a circular innervision field, comprising a holder for the blank, a plurality of buttonlocating heads supported by said holder about the outer field of saidblank, and means on said holder operable to adjust said heads to aposition thereon tangential with the circular boundary line of the innerfield to position the button within and in alignment with a portion ofsaid circular boundary line.

6. An apparatus for positioning a blanking out cam button on amultifocal lens blank having an outer vision field and a circular innervision field, comprising a holder for the blank, a plurality of buttonlocating heads supported by said holder about the outer field of saidblank, each of said heads being in the form of a truncated cone having atapered peripheral button engaging surface, and means on said holderoperable to adjust said heads to a position thereon with the base oftheir respective tapered surfaces tangential with the circular boundaryline of the inner field to position the button within and in alignmentwith a portion of said circular boundary line.

7. An apparatus for positioning a blanking out cam button on amultifocal lens blank having an outer vision field and a circular innervision field, comprising a holder for the blank, a plurality of buttonlocating heads supported by said holder about the outer field of saidblank, each of said heads having a button engaging surface and a blankengaging surface, said button engaging surface extending at an acuteangle to the blank engaging surface and parallel to the axis of theblank, and means on said holder operable to adjust said heads to aposition thereon with the base of their button engaging surfacetangential with the circular boundary line of the inner field FRANK E.DUCKWALL.

